The present invention is directed to security alarm systems, and more particularly of the type employing sensors for providing an indication of the displacement of components such as doors, windows and so forth.
Various types of security alarm systems have been implemented to detect and signify the unauthorized opening of a window, door, or other entry-exit opening. Often such arrangements include a sensor, such as a reed switch, on one component part of the door or window, and a magnet affixed to another component of the door or window. A pair of wires intercouples the reed switch or contact set with a controller, and the magnet is positioned to hold the reed switch closed when the two relatively displaceable elements are in the closed (secure) position. When the one element is displaced, the magnetic force is removed or substantially weakened in the area of the reed switch, which then opens to provide an indication over the conductor pair to the controller that the window or door has been opened. This conventional arrangement suffers from several drawbacks.
One shortcoming is that from the standpoint of a would-be burglar, such arrangements are not very difficult to circumvent. Intruders have become adept at breaking a window and then shorting the conductors leading to the reed switch, to maintain the secure indication even when the window is thereafter opened.
Another drawback of earlier systems with multiple sensors (including contact pairs) on the same conductor pair is that the controller does not recognize which sensor has gone into alarm. Various attempts to solve this problem have been made, including providing a transponder assembly for one or more sensor points to provide addressability--denoting the location(s) of the sensors in alarm. The transponder has been housed in a separate enclosure, leading to a more costly and complex wiring arrangement to achieve addressability, especially when a plurality of sensors are attached to a single transponder.
Another deficiency is that the described arrangements for addressability have been costly, requiring three separate components: the magnet, the reed switch or other sensor, and a transponder coupled between the reed switch and the controller, for incorporating a specific address denoting the physical location of a given sensor and facilitating communication between the controller and the transponder. Not only is such an arrangement costly, but the components may degrade the aesthetics of the room decor. Frequently architectural specifications militate against placing the units in the most desirable locations, and this is another drawback.
It is therefore a principal consideration of the present invention to provide a security system with an enhanced protective level, by adding new levels of complexity to thwart the would-be intruder.
Another important consideration is to provide addressability in a security system at reduced cost, with simplified installation.
Another important consideration is to provide an effective cost reduction in such security systems.
Still another significant consideration is to provide an improved security system which is more pleasing from an aesthetic standpoint.